The present invention relates generally to deflectors for tractor-trailer combinations and, more particularly, to deflectors that are deployed in response to detection of the presence of a trailer.
Commercial vehicles are one of the key contributors to fuel usage for ground transportation. The power required to propel heavy duty vehicles varies with a number of external factors but depends heavily on the speed of the vehicle. Aerodynamic drag is the predominant contributor to power requirements of such vehicles at highway speeds, but it is significant even at moderate speeds typical of urban, local or regional operation. Reducing aerodynamic drag for these vehicles would therefore yield significant reduction in power requirement and fuel usage.
The force of aerodynamic drag experienced by a vehicle moving down the road at a given speed can be calculated using the following equation:Faero_drag=½·ρ·ν2·Cd·A where:
Faero_drag is the aerodynamic drag force
ρ is the mass density of the air
ν is the velocity of the object relative to the fluid,
A is the front area of the vehicle
Cd is the drag coefficient—a dimensionless coefficient related to the object's geometry This equation shows that for a given speed, the aerodynamic drag can be reduced either by reducing Cd, the drag coefficient of the vehicle, or A, the front area of the vehicle. Trailers and containers are typically taller and wider than tractors; therefore they dictate the front area of the complete vehicle. Aerodynamic deflectors help reduce the drag coefficient Cd of tractor-trailer combinations by directing the onward wind flow smoothly to the trailer or container and thus reducing flow separation in front of the trailer or container. Aerodynamic deflectors can yield significant fuel savings at highway speeds; however, these deflectors also increase the front area of the tractor compared with the same tractor without deflectors, which will result in a fuel penalty of similar relative magnitude when not used in a tractor-trailer combination.
A tractor equipped with aerodynamic deflectors will therefore provide benefits when used in combination with, e.g., a box trailer but will be less efficient than a tractor without deflectors when used in combination with a low trailer or without trailer, and vice-versa.
It is desirable to provide a deflector arrangement that can provide advantageous aerodynamic qualities when a trailer that forms an aerodynamic drag source is attached to a tractor while not significantly adding to drag when, e.g., not connected to a trailer.
According to an aspect of the present invention, a deflector arrangement for a tractor is provided, the tractor being connectable to a trailer that forms an aerodynamic drag source. The deflector arrangement comprises a deflector, a mount for connecting the deflector to the tractor, means for selectively deploying and retracting the deflector relative to the tractor, a sensor arranged to sense that the trailer that forms the aerodynamic drag force is attached to the tractor and send a loaded signal in response thereto, and a controller arranged to receive the loaded signal from the sensor and to control the selectively deploying and retracting means to deploy the deflector in response to the loaded signal.
According to another aspect of the present invention, a tractor for a tractor-trailer combination comprises a tractor having a mount for attaching at least a trailer of a type that forms an aerodynamic drag source, and a deflector arrangement. The deflector arrangement comprises a deflector, a mount for connecting the deflector to the tractor, means for selectively deploying and retracting the deflector relative to the tractor, a sensor arranged to sense that the trailer that forms the aerodynamic drag force is attached to the tractor and send a loaded signal in response thereto, and a controller arranged to receive the loaded signal from the sensor and to control the selectively deploying and retracting means to deploy the deflector in response to the loaded signal.
According to yet another aspect of the present invention, a method is provided for adjusting an deflector of a deflector arrangement on a tractor of a tractor-trailer combination, the tractor being connectable to a trailer that forms an aerodynamic drag source, the deflector being connected to the tractor, and the deflector arrangement comprising means for selectively deploying and retracting the deflector relative to the tractor. The method comprises sensing that the trailer that forms the aerodynamic drag force is attached to the tractor and sending a loaded signal in response thereto, and controlling the selectively deploying and retracting means to deploy the deflector in response to the loaded signal.